Validation of activated sludge plant performance for virus and protozoan reduction

Validation studies were undertaken at Adelaide metropolitan wastewater treatment plants to establish the actual log₁₀ reduction values (LRVs) of pathogens (viruses and Cryptosporidium) across activated sludge plants (ASPs) as an alternative to accepting the default values attributed by the Department of Health and Ageing (DHA). Grab samples were collected across a 6-week period and assessed for pathogens (adenovirus and Cryptosporidium) and indicator microorganisms (sulphite-reducing clostridia and F-RNA bacteriophage). Through applying the validation process, the DHA has revised the default value for reduction of viruses with an increase from 0.5 log₁₀ to 1 log₁₀ while the value for protozoa remains at 0.5 log₁₀ based on the combined data for a well-operated and maintained ASP. This provides the basis for considering further work at individual plants which may allow higher log credits to be obtained on a plant by plant basis.